1. Field of the Invention
This invention relates to large diameter, low pressure vessels and, more particularly, to a novel apparatus and method for providing a uniform flow profile through a large diameter, low pressure vessel.
2. The Prior Art
Numerous processes in the chemical industry require the passage of large volume liquid streams through loosely packed beds where certain reactions occur. Importantly, many of these liquid streams involve highly sensitive components that are adversely affected by extended exposure to the constituents of the packed beds. One method for carefully controlling the exposure or contact time is to divide the large stream into a plurality of smaller streams and direct each of these smaller streams into a separate, low-pressure, packed column where the inflow rates and residence times in the column can be precisely controlled.
Ideally, the liquid flowing through the packing flows downwardly with a uniform "front" when viewed in cross section across the column. This means that at any given point along the length of the column the liquid "front" in that particular cross section of the column will be uniform in composition. The term "plug flow" has been used to describe the movement of this hypothetical "front" of liquid through the column. Clearly, of course, the term "plug flow" is somewhat of a misnomer in that it appears to imply that a "plug" of liquid flows through the column whereas in reality, the column operates under steady state conditions so that the "front" at any given point along the length of the column is uniform throughout the cross sectional area of the column although the composition with each "front" will vary along the length of the column according to the control parameters imposed on the column.
This is an important distinction for identifying the unique features of the novel apparatus and method of this invention to distinguish it over the various devices of the prior art. One series of prior art technology involves high pressure separation in small laboratory columns and reactors typically used for analytical liquid and gas chromatography. These columns may contain sorbent material coated on the interior surface area or columns which are tightly packed with finely ground ion exchange material. These columns impose a high pressure drop on the liquid passing through the column. Others include a bundle of fins radiating from the outside wall toward the center, the fins being used to act as radiators for the purpose of temperature control. The fins also impose frictional resistance and turbulence on the liquid passing through the column and thereby achieve uniform cross sectional distribution and to provide large contact area at pressures exceeding 200 psi to over 2,000 psi. To meet these objectives the interior fins must be in close proximity to each other with a separation of only a few millimeters. Small analytical laboratory columns with such fin members are typically less than one inch in diameter. Such techniques are not applicable to large diameter, commercial type columns and reactors where design limitations and costs would prohibit the use of fins in close proximity to each other and restrict operation to relatively low pressures below 200 psi and where the sorbent packing material which represents a major part of the total costs would be damaged by continuous, long term high pressure operation.
Wright (U.S. Pat. No. 3,298,527) discloses a chromatographic flow column wherein inwardly directed longitudinal fin members extend radially from the outer wall of the column toward the center of the column. These fins are used to present frictional surfaces throughout the cross section of the column. The fins are also used as radiators to facilitate temperature control in the column. The heat is supplied to the exterior column wall surface where the fins conduct the heat into the interior of the column. The moving phase travelling through an unpacked column encounters flow resistance not only at the inner periphery of the column wall but also at the surfaces of the fin members as well. Wright teaches the distribution of the fin members evenly throughout the cross section of the column. Conversely, in a packed column, when the moving phase travels through the column, a greater resistance to flow is offered at the interior portions of the granular packing material than by the packing located adjacent the column wall and adjacent the fin walls. However, since the surfaces of the fins of Wright are distributed throughout the cross section of the column, the forces tending to produce differences in flow velocity are thereby more uniformly arranged throughout the cross section of the tube, and a relatively uniform flow velocity can thus be attained. (See column 3, lines 55-65).
In summary, the reference of Wright teaches the use of uniformly distributed, inwardly oriented, longitudinal fins to provide increased flow uniformity through the frictional resistance to flow contributed by the fins. The foregoing frictional resistance to flow contributed by the fins can be accentuated by producing the column in segments and, prior to joining the segments end-to-end into a column, rotating each segment relative to the adjacent segment thus producing an offset between adjacent fins. The fins of Wright are also used to carry externally applied heat into the interior of the column.
Other references include that of Warden (U.S. Pat. No. 1,140,726) which discloses a filter wherein the filter media is disposed in spaced, concentric annular walls through which the liquid to be filtered passes in lateral flow through each concentric filter sequentially.
The reference of Piasio (U.S. Pat. No. 4,197,287) discloses a laboratory diagnostic device wherein one or more solid phase matrices are affixed to longitudinal fins mounted in a test tube. The fins provide the solid phase matrix with an increased surface area relative that which would otherwise be available if only the inner wall of the test tube were coated with the solid phase matrix. Accordingly, the surface area to volume ratio is substantially increased thereby providing a corresponding increase in the overall reaction rate for the diagnostic technique.
Bleakly (U.S. Pat. No. 607,155) discloses a filter for filtering the water of streams, lakes, etc. The filter includes a reverse flow system for cleaning the filter bed.
Shafor (U.S. Pat. No. 2,365,221) discloses a reactor vessel for conducting ionic exchange operations wherein a floating distributor plate is supported on the top surface of the ion exchange resin bed. The distributor plate uniformly distributes the liquid undergoing treatment in the resin bed across the top surface of the resin bed.
Numerous filters, distillation columns, reactor vessels, and chemical processing strategies are known throughout the industry. However, what is needed is an apparatus for providing a uniform flow profile through a large diameter, low pressure vessel. It would also be an advancement in the art to provide improvements in methods for passing a liquid stream through a large diameter, low-pressure vessel wherein the liquid passes with a uniform frontal passage with minimal lateral movement of the liquid within the theoretical front. Such a novel apparatus and method is disclosed and claimed herein.